The present invention relates to hybrid drive systems for motor vehicles. More specifically, the present invention relates to an integrated electric motor and axle assembly for use in hybrid motor vehicles.
Automobile manufacturers are actively working to develop alternative powertrain systems in an effort to reduce the level of pollutants exhausted into the air by conventional powertrains equipped with internal combustion engines. Significant development has been directed to electric vehicles and fuel cell vehicles. Unfortunately, these alternative powertrain systems suffer from several disadvantages and, for all practical purposes, are still under development. However, several different hybrid electric vehicles (HEV) have recently been offered for sale. These hybrid vehicles are equipped with an internal combustion engine and an electric motor that can be operated independently or in combination to drive the vehicle.
There are two types of hybrid vehicles, namely, series hybrid and parallel hybrid. In a series hybrid vehicle, power is delivered to the wheels by the electric motor which draws electrical energy from the battery. The engine is used in series hybrid vehicles to drive a generator which supplies power directly to the electric motor or charges the battery when the state of charge falls below a predetermined value. In parallel hybrid vehicles, the electric motor and the engine can be operated independently or in combination pursuant to the running conditions of the vehicle. Typically, the control strategy for such parallel hybrid vehicles utilizes a low-load mode where only the electric motor is used to drive the vehicle, a high-load mode where only the engine is used to drive the vehicle, and an intermediate assist mode where the engine and electric motor are both used to drive the vehicle. Regardless of the type of hybrid drive system used, hybrid vehicles are highly modified versions of conventional vehicles that are expensive due to the componentry, required control systems, and specialized packaging requirements.
Hybrid powertrains have also been adapted for use in four-wheel drive vehicles and typically utilize the above-noted parallel hybrid powertrain to drive the primary wheels and a second electric motor to drive the secondary wheels. Obviously, such a four-wheel drive system is extremely expensive and difficult to package. Thus, a need exists to develop hybrid powertrains for use in four-wheel drive vehicles that utilize many conventional powertain components so as to minimize specialized packaging and reduce cost.
It is an object of the present invention to provide a hybrid powertrain drive system for a four-wheel drive vehicle.
It is another object of the present invention to provide an integrated gearbox and electric motor assembly for use as an electric drive motor axle in a hybrid vehicle.
As a related object, the hybrid drive system of the present invention utilizes an internal combustion engine as a first drive source to supply motive power to a first set of wheels and further uses the electric drive motor axle as a second drive source to supply motive power to a second set of wheels. A control system functions to control operation of the first and second drive sources either independently or in combination was dictated by the current vehicle operating conditions.
These and other objects are provided by an electrically-powered drive axle adapted for use in hybrid vehicles and having an electric motor and a gearbox packaged within a common housing assembly. The gearbox includes a differential assembly driven by a planetary-type reduction unit. The reduction unit includes a sun gear driven by the motor, a first ring gear fixed to the housing assembly, a second ring gear, and compound planet gears rotatably supported from a planet carrier. Each compound planet gear has a first gear segment that is meshed with the first ring gear and a second gear segment that is meshed with the sun gear and the second ring gear. As such, the second ring gear is driven at a reduced speed relative to the sun gear and acts as the input to the differential assembly.
In accordance with one aspect of the present invention, the differential assembly is a bevel-type unit having the second ring gear driving a differential case which rotatably supports pinions that are meshed with first and second side gears. The side gears are fixed to corresponding first and second output shafts that are adapted for connection to a pair of wheels. Alternatively, the differential assembly can be a planetary-type unit wherein the second ring gear drives a third ring gear which, in turn, drives meshed sets of first and second pinion gears. The first and second pinion gears are rotatably supported from a pinion carrier which is fixed for rotation with a first output shaft. The meshed sets of first and second pinion gears drive second sun gear which is fixed for rotation with a second output shaft.
In accordance with an alternative aspect of the present invention, the reduction unit can be arranged to eliminate the sun gear and have the planet carrier driven by the motor.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the present invention, are intended for purposes of illustration only since various changes and modifications within the fair scope of this particular invention will become apparent to those skilled in the art.